The present invention relates to a detectable element for enabling a detector to detect the passage or presence of an object to which the detectable element is attached.
There has been proposed a detectable element which comprises a small permanent magnet that can be attached to an object to be detected. When the object with such a permanent magnet attached reaches a certain location, the magnetic flux emanating from the permanent magnet is detected by a detector so that arrival of the object at the location or passage thereof through the location can be ascertained. Such detectable elements have found a wide variety of applications. For example, the detectable elements are applied to goods displayed for sale in a retail store. When someone who has shoplifted one or more of such goods walks through an entrance or exit of the store, they can immediately be detected by a detector installed at the entrance and exit.
The detectable elements for such crime-prevention use are required to be extremely small in size since, when attached to goods, they should go unnoticed. The small-size detectable elements generally produce a relatively weak magnetic field. Products of iron which are normally present around us retain some degree of residual magnetism. The detector therefore frequently fail to clearly distinguish goods to which the detectable elements are attached from those products of iron with such residual magnetism which happen to approach or pass by the detector. External magnetic noise generated by nearby vehicles also seriously affects the detector, which then becomes unable to detect detectable elements properly.